parent drama

Hey guys !! So I just turned 18 a few months ago, I work ( which I have done for the past four years ), I just started university, I pay rent each week and do chores. But none of this is good enough for my mum. She isn't happy with the fact that I only work six X 5 hour shifts a week,    And is forcing me to find a job with more hours. When I tell her I am happy with my job and I don't want to put more stress on to me with my studies she doesn't accept that. She says I do nothing all day and never sees me study, even tho I'm on distinctions (2nd highest grade you can get)  for all my work and she gets home at 5:00pm. I also pay rent, buy my own food, toiletrys and clothes and never ask for anything yet she acts like I'm doing nothing ???? Acts like I'm doing the bare minimum, just scrapping by. I don't know what more I can do, I work I study and I pay rent. Can someone please help :(